This invention relates to a fiber for lateral beaming of a laser beam, and more particularly to a fiber for lateral beaming of a laser beam wherein an affected portion in a cavity of an internal organ in a living body is irradiated sideways by the laser beam in a through-endoscopic manner.
The techniques of medical treatment for conducting diagnosis and treatment of an affected portion such as a tumor in a cavity of an internal organ in a living body by laser beam irradiation in a through-endoscopic manner have been clinically put into practice by rapid progress in laser techniques and the technique of the light transmitting fiber. The fibers for introducing the laser beam into a cavity in an internal organ in a living body to irradiate the affected portion include a fiber for front beaming having a distal end face perpendicularly intersecting the longitudinal direction of the fiber, and a fiber for lateral beaming exiting at a right angle through the side surface of the fiber. When an affected portion in a narrow cavity in an internal organ such as a gullet, a trachea or a bowel is irradiated by the laser beam, it is preferable that the irradiation energy received by the affected portion be uniform on the affected portion as a whole. For this purpose, a fiber for lateral beaming for irradiating in a direction perpendicular to the wall of the cavity, i.e. for frontally irradiating the affected portion, has been proposed in Japanese Application No. 187782/1984 by the present applicant. The fiber for lateral beaming disclosed in this Patent Application No. 187782/1984 is constructed such that a distal end is formed to provide a surface inclined at about 45.degree. to the center line of the fiber. Further, this inclined surface is formed by coupling thereto a transparent tubular member blocked at one end thereof in a manner not to include an acute angle portion, and air layer is formed behind the inclined surface of the distal end of the fiber to obtain an entirely reflecting surface, whereby the laser beam transmitted through the fiber is refracted in a direction perpendicular to the longitudinal direction of the fiber, so that the laser beam exits from the side surface of the fiber.
To explain in further detail, FIG. 6 shows a sectional view illustrating the above-discussed fiber for lateral beaming of the laser beam, wherein a fiber 11 is a light-transmitting fiber made of glass or plastics and constituted by a core and a clad which are different in refractive index from each other. In this case, the fiber is a quartz fiber having a core diameter of 400 .mu.m and an outer clad layer diameter of 650 .mu.m. A primary coating layer 12 made of a synthetic resin material is formed on the fiber 11 over the total length thereof. The fiber 11 formed thereon with the primary coating layer 12 is further protected by a flexible, protective outer covering jacket 13, whereby the fiber 11 is prevented from being cracked and broken. Synthetic resin materials such as vinyl resin material, nylon and Teflon are prefearbly used to form this protective outer covering jacket 13.
To refract and exit the laser beam transmitted in a direction perpendicularly intersecting the longitudinal direction of the fiber, a distal end of the fiber 11 is formed to provide a flat surface 14 inclined at about 45.degree. to the center line of the fiber 11, and this flat surface is polished into an optically smooth surface. Portions of the primary coating layer 12 and protective outer covering jacket 13 are removed from a portion of the fiber 11, including the distal end which is formed into the flat surface 14 inclined at about 45.degree. to the center line of the fiber as described above. The side of the distal end of the fiber 11, from which the primary coating layer 12 and protective outer covering jacket 13 are removed, is coupled to a transparent tubular member 15 of circular cross section. One end of tubular member 15 is blocked in a semispherical shape, and the distal end and the tubular member 15 are firmly attached to each other in an air-tight manner by an epoxy adhesive 30. The inclined flat surface 14 of the fiber 11 is disposed in this transparent tubular member 15 such that an air layer 32 is formed between the inner surface of the tubular member 15 and the inclined flat surface 14 of the fiber 11. A stepped portion 18 is formed at the side of the open end of the transparent tubular member 15 over the entire circumference thereof. The forward end portion of a reinforcing tube 19, made of a flexible material such as Teflon for protecting and reinforcing the fiber 11 substantially over the total length thereof, is solidly secured to this stepped portion by adhesive bonding, or by being enlarged in diameter due to heating and coupled onto the stepped portion, and thereafter cooled for shrinkage. This reinforcing tube 19 is provided with an inner diameter sufficient for forming a hollow space 21 which is annular in cross section and extends between the inner peripheral surface thereof and the protective outer covering jacket 13 of the fiber 11 over the total length, and with an outer shape substantially equal to the outer shape of the transparent tubular member 15. A groove 20, communicated with the hollow space 21 when the distal end of the fiber 11 and forward end portion of the reinforcing tube 19 are coupled to the open end of the transparent tubular member 15, is formed in a portion of the transparent tubular member 15.
The fiber for lateral beaming discussed above functions very effectively when it is used together with a front-view type endoscope in a through-endoscope manner. However, the following disadvantages have been presented by this fiber for lateral beaming.
Firstly, a thin air layer is formed between the inner wall surface of the transparent tubular member in the longitudinal direction thereof and the outer peripheral wall of the fiber, and the interface therebetween functions as a reflecting surface due to the presence of this air layer. As a result, a leaking beam is generated which is emitted in a direction other than aan aimed direction, particularly to a direction opposite to the aimed direction (namely in the direction of leaking). As the amount of energy thereof increases, this leaking beam results in burning a normal portion other than the aimed affected protion. To eliminate the interface reflection caused by the above-described air layer, it may be proposed to improve manufacturing accuracies of the outer diameter of the fiber and the inner diameter of the tubular member to obtain very high coupling accuracy, so that no air layer can remain between the members. However, the above proposal is not desirable from the viewpoint of suitability for mass production. Even if such a proposal is possible, it brings about very inefficient results in inserting the fiber, made of quartz or the like, and having a sharp forward end inclined at about 45.degree., straight into the tubular member without impinging against the tubular member, thus contributing to increased costs in the assembling operations.
Secondly, another leaking beam, other than the leaking beam caused by the interface of the air layer, is generated. This leaking beam is directed in the forward direction of a probe. Although it depends upon the mode of propagation of the laser beam, which has fallen into the fiber, this beam is not reflected laterally, transmitted through the surface inclined at 45.degree., and directed forward because of the presence of an incident beam component, the incident angle of which becomes lower than a critical angle on the entirely reflecting surface. Similarly to the former leaking beam caused by the interface reflection, the latter leaking beam results in burning a normal portion other than the aimed affected portion.
The third problem of which the fiber for lateral beaming which has heretofore been proposed, is the problem of breakage in use. Namely, under the use conditions in a through-endoscopic manner a fiber probe is not guided rectilinearly to the aimed position in a body, rather, it is introduced to the aimed portion in the body using an endoscope tridimensionally flexed for catching the affected portion in the visual field of observation of the endoscope as a path for the insertion of the fiber probe. As the path for introducing the fiber probe for this purpose, there is utilized a forceps channel having an inner diameter of about 2 to 3 mm for introducing a forceps for the treatment. A radius of curvature of this forceps channel in an endoscope used at present is fairly small, whereby an external force in a direction crossing the axial line of the fiber is applied to the forward end portion of the fiber having no flexibility when the fiber is passed through a curved portion having such a radius of curvature as described above. Under these conditions, as seen in FIG. 6, when a strong external force directed along the axial line is applied to the tubular member and therearound, a sharing force occurs at a boundary portion between a portion of the continuous fiber, which is covered by the inflexible tubular member, and a portion of the fiber, which is covered by the flexible coating layers and the flexible outer covering layer, whereby a breakage occurs at this boundary position. As the case may be, the portion of the fiber falls down together with the tubular member and remains in the body, so that very dangerous results may be brought about.
Further, there is a problem caused by the use conditions in a through-endoscopic manner, particularly caused by the use conditions using the front-view type endoscope. Since an aiming beam and the laser beam for the irradiation treatment should be confirmed within the visual field of the endoscope, the forward end of the fiber probe should be protruded forward from the forward end of the front-view type endoscope by a value commensurate to an angle of the field of observation of the endoscope. As this forward protrusion value increases, it becomes more difficult to change the degrees of flexing of the forward end portion of the endoscope and to finely adjust the direction of irradiation. Furthermore, if the flexing control of changing the degrees of flexing of this forward end portion is not carried out carefully and properly, there may be a danger of the forward end of the fiber probe coming into contact with the wall surface of the cavity particularly in a flexed narrow cavity. The above described contact may cause foreign material, such as mucus and blood which are secreted in the body, to adhere to the fiber probe, particularly to the tubular member. Adhesion of the above-described foreign material results in absorption of the laser beam, generation of heat, and finally burning.